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Planetary exploration Spaceflight Vol 47 July 2005 Mapping the planet Mars Ancient Babylonian clay tablets depicted the Earth as a flat circular disk but both Roman, Greek and Arab empires’ cartographers were more interested in producing celestial globes rather than terrestrial. The first terrestrial globe was produced by Crates of Mallos, around 150 BC, and the earliest surviving Earth globe was produced by Martin Behaim in 1492. However, it lasted until the 20th century when the first photos of Earth from space to produce the most accurate terrestrial globes. Since then mankind’s attention has turned to the planets. Mars before the space age The planet Mars, named after the Roman god of war, is fourth in order of distance from the Sun and seventh in order of size and mass. The astronomical symbol for Mars, represents a shield with a spear. The socalled red planet is slightly more than half the size of Earth but the lack of oceans gives it the same landmass as Earth. Mars has no Lowell observatory – Flagstaff Arizona by Philip Corneille plate motion and its rotational axis is inclined to the ecliptic, like Earth’s. The planet completes an elliptical orbit around the Sun in 687 days and spins on its axis with a period of 24 hours 37 minutes. This period is named a ‘sol’ or Martian solar day. It has two moons, Phobos (Fear) and Deimos (Terror), named after the mythical chariot horses of Mars. The inner moon, Phobos, is already within the ‘Roche limit’ where internal gravity alone is insufficient to hold it together. Mars globe (top) made by Percival Lowell in 1911, based on his observations. It shows the ‘canals’ in the area of Elysium planitia and Utopia planitia and (above) Mars photo-frames show the areas covered by the 1969 fly-bys of Mariner 6 and 7. NASA/JPL Phobos could conceivably become a ring plane around the Mars within the next 50 million years. Galileo Galilei made the first telescopic observations of Mars in 1610. Another Italian astronomer, Francesco Fontana, produced the earliest drawings that showed markings on the disk of the planet. Unfortunately, these markings bear no resemblance to the planetary features known today, so the Dutch scientist/astronomer Christiaan Johann von Mädler in 1830. It featured a system of longitude and latitude, not too different from today’s coordinate system. In 1877, the American astronomer Asaph Schiaparelli is usually credited with their first description. However, the idea of ‘canals’ might have originated in the work of the Italian Huygens was credited with the first accurate Hall discovered Mars’ two tiny moons and astronomer Angelo Secchi of the Vatican drawings with surface details of Mars (1659). the Italian astronomer Giovanni Schiaparelli observatory (1868). When Schiaparelli had In 1666, the Martian polar caps were first produced the first modern map of Mars, which contained Latin nomenclature in terms to abandon his observations, a wealthy Boston aristocrat, Percival Lowell, decided to of the ancient geography of the continue the work and set up an observatory Mediterranean area in biblical times. The atop ‘Mars hill’, Flagstaff, Arizona in 1894. map showed indications of grooves or The dedicated amateur astronomer was channels on the bright areas and convinced that the ‘canals’ on Mars were noted by Giovanni Cassini, who also calculated the rotation period of the red planet. The very first map of Mars was made by German astronomers Wilhelm Beer and 270 Planetary exploration built by an intelligent civilization on the red planet. Lowell made maps and Mars-globes based on his 15 year long observations and published his views in three books: ‘Mars’ (1895), ‘Mars and its canals’ (1906) and ‘Mars as the abode of Life’ (1908). Although controversial, Lowell’s maps were widely used until the 1950s when photographic advances were hoped to resolve some differences but even photographs were subject to interpretation. It lasted until 1958 for the International Astronomical Union (IAU) to adopt a formal list of place-names on Mars related to a Mars-map by Glauco de Mottoni, which was based on a large number of photographs taken by the French astronomer Henri Camichel at the Pic du Midi observatory. Confidence in visual observation remained strong until telescopic views of Mars were replaced by high-resolution space probe images. Finally in July 1965, the Mariner 4 fly-by ended an era of Mars studies limited to Earth-based observations. Mars-mapping from spacecraft NASA’s Jet Propulsion Laboratory (JPL) Three large four foot diameter photomosaic globes are completed with Mariner 9 pictures. Each picture underwent many stages of computer processing and photographic printing. NASA/JPL The Mariner 9 photomosaic Mars globe showing the consistency of the tone and contrast of the photographs. A specially designed protractor that swivelled around the poles was used to locate each picture. NASA/JPL Mariner Mars project started the initial exploration of Mars when the Mariner 4 fly-by provided the first views of the Martian surface (see page 270). The Mariner 4 television experiment showed cratered terrains and proved to be historic and scientific significant but the pictures could not contribute to a clear understanding of transient features. The 1969 fly-bys of Mariner 6 and 7 returned about 200 times the picture data of Mariner 4 and these probes also provided low-resolution coverage of the entire planet by acquiring full disc views of Mars using the high-resolution camera before closeencounter. However, these remarkable farencounter global photographs were insufficient to create an accurate complete globe of the red planet. Altogether, the Mariner 4, 6 and 7 fly-bys only photographed 10 percent of the surface of Mars. A complete mapping of the red planet was performed by the Mariner 9 spacecraft, which went in orbit around the planet in November 1971. The spacecraft’s mission was to map 70 percent of the surface of Mars during 90 days in orbit but Mariner 9 remained operational for 349 days and mapped the complete surface of Mars. It also photographed the Martian moons Phobos and Deimos. After nearly one year of operation, Mariner 9 returned 7300 photos, which 271 Planetary exploration Spaceflight Vol 47 July 2005 Mariner 4 – During the November 1964 launch window to Mars, both Russia and America sent unmanned spacecraft to the red planet. After the Russians lost contact with their Zond-2 in April 1965, it was the American Mariner 4 which, in July 1965, became the first interplanetary spacecraft to successfully flyby Mars and send back photos. Mariner 4 spacecraft NASA approved the Mariner-Mars project in November 1962 and the Jet Propulsion Laboratory (JPL) started to build the twin Mariner 3 and 4 spacecraft. These were based on Mariner 2 but with four solar panels. The two large four foot diameter globes being produced based on the 1971 Mariner 9 mapping pictures. Mariner 9 circled Mars 698 times and returned 7300 photographs. NASA/JPL The 261 kg Mariner 4 carried seven scientific instruments, most of which were mounted on the outside of the revealed a planet beyond speculation. The a 6-foot diameter globe for the von Karman frame, a Helium magnetometer, a solar- images showed astonishing geological auditorium of the JPL campus in Pasadena, plasma probe, a trapped radiation features such as giant volcanoes, plateaus California. Completed in September 1973, detector, a cosmic ray telescope, a and the largest canyon in the solar system, these globes showed large-scale geologic named “Valles Marineris” in honour of its discoverer. features with a perspective that scientists couldn’t obtain on flat projections. micrometeorite detector, an ionisation chamber and Geiger-Muller tube to More surprisingly, after computer The next generations of spacecraft sent measure radiation. Last but not least, Mariner 4 was processing of the digital TV images, subtle to Mars had cameras (vidicons) with vastly equipped with a television camera details such as the relics of ancient improved capabilities. The 1976 Viking capable of taking 22 black-and-white riverbeds and gullies were revealed in the orbiters photographed 95 percent of the landscape of this seemingly dry and dusty planet. These enhanced high resolution surface at a resolution of 200 metres. The 1997 Mars Global Surveyor orbiter cameras photographs through a small Cassegrain telescope mounted on a photographs enabled JPL to produce the first made wide-angle images of the Martian photo-mosaic globes of a planetary body. surface and data from the spacecraft’s laser scan platform at the bottom centre of the spacecraft. altimeter have given scientists their first 3-D Eight month journey mosaicing of the four-foot globes was views of Mars’ north polar ice cap. The 2001 After two years of preparation, Mariner 3 assigned to Elmer Christensen, who designed the protractor to precisely locate Mars Odyssey’s camera system obtained the most detailed complete global maps of Mars was launched on 5 November 1964 by an Atlas-Agena. However, about 50 the images on the sphere. Each Mariner 9 ever, with daytime and night time infrared minutes into flight, the spacecraft mapping picture was produced in one of images at a resolution of 100 metres. unsuccessfully attempted to deploy its The task of planning and supervising the three projections: ‘Mercator’ for the The 2004 Mars Express high-resolution solar panels and eight hours later the equatorial latitudes, ‘Polar stereographic’ for stereo camera is capable of 10 metre per spacecraft battery ran out of power. A the polar regions and ‘Lambert’ for the intermediate regions. The JPL team carefully pixel resolution and the reconnaissance task is to observe half of the surface at this later investigation indicated that the cylindrical fibreglass-honeycomb nose positioned 1500 photographs on the globe. resolution and 1 percent of the surface at 2 fairing, designed to protect the metre per pixel resolution. spacecraft during launch and ascent, Known variations in the Mariner 9 camera response were removed, along with After 40 years of reconnaissance, failed to be jettisoned, a problem solved geometric distortions and reference marks. exploration and intensive study it certainly before the end of the Mars launch Surface detail enhancement allowed ridges and craters to be seen with equal clarity in seems that mankind is ready to make the dream of a human mission to Mars come window. The Atlas-Agena launch vehicle had been fitted with a complete new the dark regions and on the bright polar true. magnesium fairing, constructed in record The author thanks Lowell observatory in Flagstaff – Arizona for the Lowell globe picture and Russell Castonguay of Anteon for providing the NASA-JPL Mariner 9 globe photographs. time by the JPL engineers, and Mariner 4 caps. The completed four foot globe was sprayed with a clear coating to protect the surface. The original globe was rephotographed in 452 roughly rectangular segments, which allowed the construction of 272 was launched on 28 November 1964. This time the launch procedure was successful and the restartable Agena Planetary exploration the first flyby of Mars stage put the spacecraft on course to the for nine hours. Then the CC&S turned off red planet. A single midcourse correction the cruise science and began the was made on 5 December 1964 to ensure playback mode, in which engineering that the probe would pass within 10,000 telemetry would alternate with playback km of the planet’s surface. The 1964 of the TV pictures data. Mariner Mars spacecraft was the first space mission to use a star (canopus) as On 15 July, JPL received the first signals. The 22 photographs stored on a navigational reference object as, during magnetic tape were transmitted to Earth its flight, Earth would transit across the at a speed of eight bits per second. Each face of the Sun. image had a size of 250000 bits, so it took April 1965 was a period of records – nine days before the full set arrived at the Mariner 4 broke both the record of continuous operation (129 days Pasadena centre. Mariner 4’s pictures comprised of 200 previously set by Mariner 2 to Venus) and TV lines with 200 picture elements per the record for long-distance radio line, each represented by 64 shades of communications (62 million miles grey from white (0) to black (63). previously set by Zond-1 to Venus). En Afterwards the photographs were route to Mars, the unmanned spacecraft detected the effects of solar flares and computer-enhanced by stretching the intensity values in order to make feature measured cosmic radiation. identification easier. By 7 July, Mariner 4 had entered the The first, historical image showed 350 gravitational field of Mars and four days km of the 15,000 km far Martian limb at later it was only one million miles away. about 40° North latitude. On 14 July 1965 the signal was sent to aim the cameras at the Martian surface The most significant finding from the 22 close-up Mariner 4 photos was the fact and Mariner 4 began photography when that Mars appeared much more Moon-like the spacecraft was 9000 km above Mars’ than Earth-like as the surface was heavily surface. cratered. More than 70 craters appeared The television subsystem worked in the Mariner 4 pictures. correctly, filled its magnetic tape with 22 pictures, shut itself off and ordered the Although the spacecraft couldn’t give any definite data on the possibility of telemetry system into cruise mode in extra-terrestrial life forms on Mars, from order to activate the science instruments. the data returned by the spacecraft’s One of the great achievements of the instruments scientists concluded that no Mariner 4 mission was the modification of form of life existed. mission plans while the spacecraft was in transit in order to accommodate certain Mariner 4 was not expected to survive much longer than the eight months after science experiments. The mission had its flyby, but actually lasted about three been designed to occult Mariner 4 behind years in solar orbit, continuing long-term the planet so that the effects of the studies of the solar wind environment Martian ionosphere and atmosphere on and making coordinated measurements the spacecraft’s radio signals could be observed. Not only did the experiment with Mariner 5, a sister ship launched to Venus in 1967. indicate surface pressures of 4.1 to 7.0 Radio-tests on the Mariner IV spacecraft. Compare the size of the craft against the JPL-engineers. Photos: NASA/JPL Side-view of Mariner IV clearly showing the TV camera underneath the octagonal structure. The ‘Venetian blinds’ on the sides were used for internal temperature control. Mariner IV is being readied for its historical mission to Mars in 1964. The 1965 flyby of Mars emphasised the mbar but it also confirmed the benefits of exploratory potential of space maintaining some flexibility in mission photography. Although only one percent plans even after a spacecraft is launched. of the Martian surface was pictured, and The close flyby of the Mariner 4 spacecraft past Mars, combined with the the photos returned by Mariner 4 dashed the hope of finding life forms on Mars, accurate tracking of the spacecraft on its scientists convinced NASA to conduct a trajectory, allowed improvements in the more thorough exploration with orbiting calculation of the planet’s mass. Mariner missions. The greatly improved images of 4’s magnetometer discovered no Mariner 9 (1971) led to the revitalisation magnetic field and the spacecraft continued sampling the space of interest in Mars as a place where life might have harboured at some time, if not environment just outside the orbit of Mars in the present. 273 Planetary exploration 274 Spaceflight Vol 47 July 2005